1. Field of the Invention
The present invention pertains in general to the field of thrust bearings. Such bearings are frequently incorporated into the overall bearing structure for rotary equipment such as a rotating shaft. Such a shaft typically carries a rotary device at at least one end thereof, and depending upon the nature of this device, the axial or thrust loading on the shaft may be quite high. It is conventional to introduce a suitable lubricant such as oil under pressure into the bearing space defined by the opposed relatively rotating faces of the thrust bearing. The pressurization of the lubricant significantly increases the load carrying capacity of the thrust bearing by virtue of what is sometimes referred to as a "hydrostatic" effect. However, in many types of rotary devices there are relatively large variations in the magnitude of the thrust load during operation. For example, where the rotary equipment carried by a rotating shaft includes one or more fluid handling rotors, such as the rotors of turbo-expanders, compressors, or the like, there may be transient surges or increases in the thrust loading, and such increases may be both large and sudden. Because dimensional and speed limitations prevent the use of thrust bearings large enough to carry the greatest anticipated emergency loads resulting from such fluctuations, it is necessary to provide some means for preventing damage and/or malfunction of the thrust bearing during such surges.
2. Description of the Prior Art
U.S. Pat. No. 3,895,689 is exemplary of a prior art system for dealing with varying thrust loads in a rotary fluid handling device such as a turbo-expander or compressor. This system employs the technique of using measurements of the lubricant pressure within the thrust bearings as an indication of the thrust loading thereon, and further using such measurements to control a mechanism for selectively venting process fluid from the back or closed end of the rotor. Since process fluid in the latter location can act on the adjacent rotor as if it were a piston, such mechanism basically serves to offset or eliminate the cause of the thrust load surge. However, this mechanism may not relieve the excess thrust loading with sufficient rapidity to fully protect the thrust bearing upon the inception of the thrust surge.
On the other hand, faster acting thrust control mechanisms, such as air actuated instruments, may involve other problems such as hunting or overshooting of the correct thrust control adjustment. Furthermore, if the actuating air for such mechanism should fail, the mechanism may swing to its maximum or minimum correction. Thus, the thrust bearing may still not be adequately protected against damage and/or malfunction.